The present invention relates generally to a loop transmission system having double loops, and, more particularly, to a loop transmission system which can effectively bypass disordered elements to continue transmission.
A single loop transmission system cannot be used as a whole if even a partial malfunction exists in its loop. Therefore, such single loop systems are low in reliability. In order to enhance the reliability of the transmission system, according to the prior art, the loop-shaped transmission route is doubled, and transmission control units are arranged in the doubled respective transmission routes. The data transmission between terminal units is performed through such transmission control units. When the transmission system as a whole is normal, both the loops are used independently of each other so that the transmission is performed between the terminal units. Further, methods have also been developed to bypass a disordered portion of the transmission route when the transmission system is partially disordered. According to the method thus proposed according to the prior art, however, if one of the loops is abnormal while the other is normal, some of the transmission control units which remain normal may also become incapable of performing the data transmission.